Engine cylinder chamber valves are typically poppet type valves. These poppet type engine valves are normally biased closed by a valve spring. The valves open when sufficient force is applied to overcome the spring force. There are many different methods of generating valve opening force. Many valve actuation systems utilize hydraulic pressure. These systems typically include a master and slave piston arrangement The slave piston contacts the valve stem of the engine valve. Motion of the master piston generates an increase in hydraulic pressure on the slave piston. In response to the increased hydraulic pressure, the slave piston moves forcing the engine valve open.
The master and slave pistons are hydraulically linked. In such systems, a rotating cam typically causes the displacement of the master piston. The motion of the master piston is transferred to the slave piston by means of the hydraulic link between the two pistons. The motion of the slave piston, relative to the cam profile, may be modified by draining and filling the hydraulic link between the master and slave pistons. This process provides for transferring selected portions of the master piston's motion, i.e. the cam profile, to the slave piston. A system capable of transferring only a portion of the motion is commonly called a "lost motion" system. An example of such a system is described in Hu, U.S. Pat. No. 5,537,976, assigned to the assignee of the present application and incorporated herein by reference.
Lost motion systems may be used to vary engine valve timing. In order to achieve enhanced internal combustion engine performance and fuel economy, it may be necessary to vary the timing of the engines intake and exhaust events. It may be desirable in engines having multiple intake and/or exhaust valves per cylinder to effect staggered opening among the valves in a cylinder. It also may be desired to operate a four valve cylinder in either a two valve or four valve mode. Additionally, it may be necessary to "cut-out" the cylinder. Cylinder cut-out can be achieved by failing to actuate all of one cylinders, intake, and exhaust valves. A valve actuation system which is capable of varying the cylinder operation from all valve operation to cylinder cut-out is termed a fully variable system. Fully variable valve actuation systems are also known as "full authority" systems.
As discussed above, the typical valve actuation system utilizes a cam to impart motion to a master piston. However, recent efforts to achieve variable control over intake and exhaust valve events have focused on camless engine designs. An example of a camless engine is disclosed in U.S. Pat. No. 5,619,965, which is incorporated herein by reference. Camless engine designs have proved to be difficult and expensive to implement. A further disadvantage of many camless designs is the lack of any mechanical backup. The failure of electric power or loss of hydraulic pressure may result in no valve motion at all. In fact, even some cam-driven designs cannot produce valve motion in the event of a loss of hydraulic pressure. These systems lack a fail-safe operating mode.
There is a need for a lost motion variable valve actuation system which provides control of an engine cylinder's intake and an exhaust valve using a common trigger valve. Current valve actuation systems typically rely on a single trigger valve for each engine valve. The few systems which utilize a single solenoid to control multiple engine valves, do not have the capability to independently control the positions of the valves. There is also a need for a valve actuation system which has the practical benefits of a fully variable system with the security and reliability of a mechanical, cam-driven valve train, and with the advanced system features commonly available in camless engine designs.
The present invention provides a means for controlling the engine valves in an internal combustion engine cylinder having multiple intake and/or exhaust valves utilizing a novel electro-hydraulic valve actuation system. By pairing an intake and exhaust valve under the control of a single hydraulic solenoid, or trigger, valve, independent control of each valve may be obtained, allowing for such features as enhanced intake air swirl, two-valve operation over a certain speed range, and staggered valve opening. This is possible since in most cases, relevant intake and exhaust events occur at different times in a four-cycle engine. Thus, at any given time, only one of the two valves in a set (either the intake or the exhaust) is active, with the other at base circle. Opening the trigger valve at such time would only affect the valve driven by the cam lobe off base circle at that instant. Events which overlap significantly, but which need independent control, can be placed on different cams (i.e., on one of two exhaust cams in a dual-overhead cam system with discrete lobes for each valve).